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Note 14 - Quarterly Financial Information (Unaudited) (Tables) | 12 Months Ended
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Dec. 31, 2018
Notes Tables |
Quarterly Financial Information [Table Text Block] |
|  | Quarter |
|  | First |  |  | Second |  |  | Third |  |  | Fourth |
2018: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  | $ | 1,948,245 |  |  | $ | 2,139,027 |  |  | $ | 2,209,760 |  |  | $ | 2,317,842 |
Operating income |  | $ | 168,781 |  |  | $ | 214,812 |  |  | $ | 174,688 |  |  | $ | 122,740 |
Net earnings |  | $ | 118,142 |  |  | $ | 151,652 |  |  | $ | 131,110 |  |  | $ | 88,681 |
Basic earnings per share |  | $ | 1.08 |  |  | $ | 1.39 |  |  | $ | 1.20 |  |  | $ | 0.81 |
Diluted earnings per share |  | $ | 1.07 |  |  | $ | 1.37 |  |  | $ | 1.19 |  |  | $ | 0.81 |
2017: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Operating revenues |  | $ | 1,629,158 |  |  | $ | 1,726,915 |  |  | $ | 1,843,334 |  |  | $ | 1,990,160 |
Operating income |  | $ | 149,389 |  |  | $ | 163,615 |  |  | $ | 164,972 |  |  | $ | 145,814 |
Net earnings |  | $ | 102,702 |  |  | $ | 97,869 |  |  | $ | 100,385 |  |  | $ | 385,308 |
Basic earnings per share |  | $ | 0.93 |  |  | $ | 0.89 |  |  | $ | 0.92 |  |  | $ | 3.51 |
Diluted earnings per share |  | $ | 0.92 |  |  | $ | 0.88 |  |  | $ | 0.91 |  |  | $ | 3.48 |

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- Definition Tabular disclosure of quarterly financial data. Includes, but is not limited to, financial information for fiscal quarters, cumulative effect of a change in accounting principle and earnings per share data. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 270 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=109225645&loc=d3e1280-108306 + Details
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